This invention deals with a disposable hypodermic syringe of the type which is rendered unusable after it has been used once, comprising a tube, with its front part narrowed and adapted to receive a hypodermic needle, and a hollow piston, which slides through the inside of the tube. In this front inside part of the tube, there are also obturating devices which are laid across and held in an operative position by the head of the needle. The head of the needle is in turn pressed by a spring which tends to push it towards the inside of the tube, where it is held by interlocking retention devices placed in the front inside part of the tube. There is also a device with irreversible joining retention appliances, which closes the cavity of the piston, and which will work together with other complementary joining devices on the head of the needle when they come into contact once the piston has completed its operative run.
The use of disposable hypodermic syringes which are sold in sterilized and sealed packages of one unit each and which are broken and thrown away after they are used once, is well known.
However, although these syringes are made and sold to be used only once, the truth is that their structural characteristics allow their repeated use without any difficulty from the mechanical point of view, although this gives rise to obvious and very serious problems in the area of health.
These problems have become more acute recently, since the appearance of AIDS, which eventually causes the death of the patient, and for which there is still no known cure or vaccination which will stop it from spreading.
Although there have been attempts to come up with disposable syringes to avoid their repeated use, the only ones which really work are those which, automatically and without any subsequent handling by the user, prevent any further use.
Among all the ones known which are really very few, the most efficient one is the syringe described in Spanish Patent No. 8900179, which belongs to the present invention where, as the piston completes its operative run, it springs a mechanism which automatically introduces the needle into an axial cavity inside the piston, making the removal of the needle from this cavity impossible. This action is complemented in such a way as to prevent the removal of the piston from the inside of the syringe's tube, thus making further use impossible.
However, although the general principle set out in the aforementioned Spanish Patent No. 8900179, is of great effectiveness, the Spanish patent's description of the way in which the syringe is made refers to a syringe made up of a great number of parts, which implies an increase in the costs of manufacture.